Three-dimensional (3-D) ultrasound images of the heart are useful in many catheter-based diagnostic and therapeutic applications. Real-time imaging improves physician performance and enables even relatively inexperienced physicians to perform complex surgical procedures more easily. Three-dimensional imaging also reduces the time needed to perform some surgical procedures.
Methods for 3-D mapping of the endocardium (i.e., the inner surfaces of the heart) are known in the art. For example, U.S. Pat. No. 5,738,096 to Ben-Haim, which is assigned to the assignee of the present invention, and whose disclosure is incorporated herein by reference, describes a method for constructing a map of the heart. An invasive probe or catheter is brought into contact with multiple locations on the wall of the heart. The position of the invasive probe is determined for each location, and the positions are combined to form a structural map of at least a portion of the heart.
In some systems, such as the one described by U.S. Pat. No. 5,738,096 cited above, additional physiological properties, as well as local electrical activity on the surface of the heart, are also acquired by the catheter. A corresponding map incorporates the acquired local information.
Some systems use hybrid catheters that incorporate position sensing. For example, U.S. Pat. No. 6,690,963 to Ben-Haim et al., which is assigned to the assignee of the present invention, and whose disclosure is incorporated herein by reference, describes a locating system for determining the location and orientation of an invasive medical instrument.
A catheter with acoustic transducers may be used for non-contact imaging of the endocardium. For example, U.S. Pat. Nos. 6,716,166 to Govari, and 6,773,402 to Govari et al., which are assigned to the assignee of the present invention, and whose disclosures are also incorporated herein by reference, describe a system for 3-D mapping and geometrical reconstruction of body cavities, particularly of the heart. The system uses a cardiac catheter comprising a plurality of acoustic transducers. The transducers emit ultrasound waves that are reflected from the surface of the cavity and are received again by the transducers. The distance from each of the transducers to a point or area on the surface opposite the transducer is determined, and the distance measurements are combined to reconstruct the 3-D shape of the surface. The catheter also comprises position sensors, which are used to determine location and orientation coordinates of the catheter within the heart.
Typically, such systems provide an “endoscopic view”, in which a reconstructed image is presented as it would appear if viewed through a certain catheter or other probe. For example, U.S. Pat. No. 6,556,695, to Packer et al., whose disclosure is incorporated herein by reference, describes a method for producing high resolution real-time images of a heart. During a medical procedure such as endocardial physiology mapping and ablation, real-time images are produced by an ultrasonic transducer inserted into the heart. A high resolution heart model is registered with the acquired real-time images and is used to produce dynamic, high resolution images for display during the procedure. Different parts of the anatomy may be viewed by moving a catheter distal end to “aim” an acoustic transducer at structures of interest. A joystick may be used to scan away from the field of view of the ultrasonic transducer when other parts of the anatomy are to be examined without moving the catheter. An orientation within the anatomic structure (e.g. heart chamber) is maintained using navigation icons as described in U.S. Pat. No. 6,049,622, to Robb et al., whose disclosure is also incorporated herein by reference.
Similarly, U.S. Pat. No. 6,203,497, to Dekel et al., whose disclosure is also incorporated herein by reference, describes a system and method for visualizing internal images of an anatomical body. Internal images of the body are acquired by an ultrasonic imaging transducer, which is tracked in a frame of reference by a spatial determinator. The position of the images in the frame of reference is determined by calibrating the ultrasonic imaging transducer to produce a vector position of the images with respect to a fixed point on the transducer. This vector position can then be added to the location and orientation of the fixed point of the transducer in the frame of reference determined by the spatial determinator. The location and orientation of a medical instrument used on the patient are also tracked in the frame of reference by spatial determinators. This information is used to generate processed images from a view spatially related to the location of the instrument.
U.S. Pat. No. 6,892,090, to Verard et al, whose disclosure is incorporated herein by reference, describes a method and apparatus for virtual endoscopy. A surgical instrument navigation system is provided that visually simulates a virtual volumetric scene of a body cavity of a patient from a point of view of a surgical instrument residing in the cavity of the patient.
Some systems display the ultrasonic catheter tip together with the ultrasound images, as a navigation and imaging guide. For example, U.S. Pat. No. 6,019,725, to Vesely et al., whose disclosure is also incorporated herein by reference, describes a 3-D tracking and imaging system for tracking the position of a surgical instrument (e.g., a catheter, probe, a sensor, needle or the like) inserted into a body, and displaying a 3-D image showing the position of the surgical instrument in reference to a 3-D image of the environment surrounding the surgical instrument. The 3-D tracking and imaging system aids a physician in the guidance of the surgical instrument inside the body.
U.S. Pat. No. 7,020,512, to Ritter et al., whose disclosure is incorporated herein by reference, describes a method of localizing a medical device inside a patient's body. AC magnetic signals of different frequencies are transmitted between points of known location outside of the patient's body and points on the medical device inside the patient's body. The transmitted AC magnetic signals are then processed to determine the position of the points on the medical device, and thus the location of the medical device. This processing includes correcting for the effects of metal in the vicinity by using the transmitted and received signals at different frequencies.
U.S. Pat. No. 7,020,512 also describes an alternative embodiment, in which a reference device is provided inside the patients' body, and the medical device is localized relative to the reference catheter. The use of signals comprising at least two frequencies may or may not be used in this relative localization embodiment, but typically are used at least to localize the reference catheter.